The present invention relates to a method, a telecommunication system, a network element of the telecommunication system and a terminal for arranging control signallings according to the preambles of the independent claims.
In telecommunication systems, in addition to the actual user data to be transmitted, such as speech information, for example, a large amount of different control information is transmitted between different parts of a network. In the telecommunication systems, a great amount of different control signalling is carried out between a terminal and a telecommunication network for identifying a user or for transmitting service requests, for example.
A purpose of mobile communication systems is to provide mobile users with wireless data transmission services. Hence, it is essential, particularly in the mobile communication systems, that a mobile communication network is aware of the location of a mobile station registered therein. Various mobility management protocols have been developed for this purpose.
In order to reduce unnecessary signalling, the mobile communication systems have typically been arranged such that in mobile terminated connections, a subscriber is paged within the area of only a few base stations. Each base station has a certain coverage area, which forms a cell. Cells form location areas, and a mobile station is paged only in the cells in the location area. Consequently, in order to obtain services from a serving base station, the mobile station must inform the mobile communication system of the location area within which the subscriber can be paged. The mobile station can carry out location update for the purpose. Location update can thus be used to update the subscriber location information in the network and possibly also to carry out other procedures. For example, a network according to a GSM system can transmit information about available services to the mobile station in connection with location update.
So-called third generation mobile communication systems have been developed worldwide. A 3rd generation partnership project 3GPP standardizes a third generation mobile communication system called a universal mobile telecommunications system UMTS based on the GSM system, which, for example, includes a new radio interface. The UMTS radio interface will be based on at least a wideband code division multiple access WCDMA technology.
FIG. 1 generally illustrates a mobile communication system, such as the UMTS system, according to the third generation principles. The development of the UMTS aims for flexibility, whereby a so-called access network AN can be connected to many different core networks CN1, CN2 and CN3. Since the core networks can vary greatly in their operation, interworking functions IWF1, IWF2 and IWF3 may be necessary between the access network AN and each core network. In connection with the present application, an access network refers to a network which provides the mobile station MS with a radio connection, in other words typically to a base station system.
As far as the core networks are concerned, the UMTS will probably, at least in part, be based on the GSM system, in which case connection management and mobility management in the UMTS will be mostly similar to those in the GSM system. The UMTS will enable circuit-switched and packet switched services. The packet-switched services can be based on a general packet radio service GPRS service in the GSM. The circuit-switched and packet-switched connections are controlled by different network elements that can thus form, at least in part, operationally separate core networks (or domains, as they can also be called). Location areas and mobility management can then also differ even though the mobile station communicates via the same access network.
Since in the UMTS system the core networks may be separate from each other, separate and possibly different control signalling functions may be necessary between each core network and mobile station for location update, for example. In connection with the present application, networks elements responsible for the circuit- and packet-switched connections in the UMTS system are treated as separate core networks. Different core networks can still operate controlled by a common network management and use common network elements, such as a home location register HLR, which comprises subscriber information.
Mobile stations are being developed for the UMTS system that can support several different core networks. In the UMTS system, one mobile station can have several simultaneous connections to different core networks, such as a circuit- and packet-switched connection, for example. The mobile station can be registered in more than one core network. Hence, it may be necessary in the UMTS system to carry out separate control signalling functions between the mobile station and a plurality of core networks for location update, for example.
In the UMTS system, the mobile station may monitor location area identifiers of several different core networks broadcast by the UMTS access network. The mobile station may then, when more than one location area changes, have a need to carry out several location updates over a short period of time. For this purpose, the mobile station reserves a radio connection for signalling from the access network and transmits a location updating message to a core network. When the location update is completed, the radio connection between the mobile station and the access network is released.
If the mobile station is to carry out location update to another core network, the radio connection must be re-established. Although the access network is common to different core networks, the radio connection must be released and re-established between different location updates. A similar procedure must also take place in substantially successive control signallings of other kinds even if the control signalling to a second core network were carried out soon after the control signalling to a first core network. This causes signalling load over the radio interface and is thus against general design objectives that try to minimize signalling over the radio interface.
An object of the invention is thus to provide a method and an apparatus implementing the method so as to alleviate the above-mentioned drawback. The objects of the invention are achieved by a method, a telecommunication system, a network element of the telecommunication system and a terminal characterized in what is disclosed in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.
The idea underlying the invention is that the connection between the access network and the terminal is not released between substantially successive control signallings between at least one core network and the terminal. The access network maintains the connection after the control signalling between the core network and the terminal for another potential need. According to a preferred embodiment of the invention, the need to maintain the connection between the access network and the terminal can be detected by means of a predetermined time limit in the terminal. A solution of the invention has the advantage that several substantially successive control signallings can be carried out without releasing and re-establishing the connection between the access network and the terminal between the signallings, which means that signalling over the radio interface at issue is reduced. The invention can particularly well be applied to different mobile communication systems providing a radio connection, in which case the terminal is a mobile station. Hence, the amount of signalling to be carried out over the radio interface can be reduced.
According to a preferred embodiment of the invention, the terminal determines the core networks to which control signallings are to be carried out by utilizing the time limit and transmits a request for maintaining the connection between the access network and the terminal to the telecommunication network. On the basis of the request, the connection will be maintained until the control signallings to all core networks have been carried out. According to preferred embodiments of the invention, the terminal can transmit to the telecommunication network information about the number of control signallings and/or core networks to which control signallings are to be carried out. The advantage achieved is that when the control signallings are directed to a plurality of core networks, the connection can be maintained in the telecommunication network on the basis of the information transmitted by the terminal only for the necessary period of time.
According to a preferred embodiment of the invention, in the telecommunication system a timer can be set to control as to how long the connection between the access network and the terminal is maintained. The connection can then be maintained only for a restricted period of time particularly in case of error situations.
Control signallings can be, for example, location updates to several different core networks. The request for maintaining the connection between the access network and the terminal can be transmitted either to the access network or the core network.